To reduce energy loss through roofs and walls, insulating materials have been mounted in the open spaces in the support structure for a long time. The insulation materials are frequently mineral or natural fiber mats open to diffusion. Early on it was recognized that a protective layer needs to be attached to the boundary surface of the insulated structure which faces the interior. The reason for this is the water vapor transport processes which are triggered, inter alia, by vapor pressure differences between the air in the room and the air on the outer side. If this transport stream is not slowed down, there is a risk of condensation forming on the inner side of the roof and/or wall structure in the cold season. Condensation can occur whenever an unretarded diffusion or convection flow encounters cold component layers, because air can hold less and less water with decreasing temperature. In the worst case, the air present in the cross-section of the building component can become oversaturated, such that significant amounts of excess water are removed from the air as condensation.
In central and northern Europe, the condensation risk occurs mainly in winter, when there is high vapor pressure indoors and low vapor pressure in the air outdoors. For this reason, an attempt is made to block the diffusion current at the side facing into the room, i.e., the warm side of the structure—in order to block the access of the moist air to the structure, which, in the form of rafters or support structures, has a function which affects safety.
Bituminous paper and aluminum coated papers are known from the prior art, and are termed “vapor barriers.” Today, plastic films are predominantly used.
In diffusion-inhibiting films known from the prior art, the diffusion resistance Sd values reach approximately from 2 m up to 150 m, and for aluminum films even up to >1500 m, which corresponds to vapor impermeability within the physical context of buildings. The higher the Sd value is, the greater the diffusion resistance. The most commonly used, however, are films with Sd values around 100 m.
In addition to films, OSB boards or gypsum plasterboard panels are used as airtight layers and diffusion-inhibiting layers on the inner side. Their Sd values, however, are very low, so they often cannot sufficiently oppose the diffusion current.
In central Europe, diffusion-inhibiting materials are used on interior sides, whereas materials which are open to diffusion are more commonly used on the exterior sides to allow moisture which can occur in the cross-section of building components to diffuse outward.
All materials listed above have a largely constant Sd value which depends only on the water vapor diffusion resistance value as a characteristic value of the material, and the layer thickness of the material. The water vapor diffusion equivalent air layer thickness in this case is little influenced by ambient conditions such as temperature or humidity.
Vapor retarders are known from the prior art, the resistance of which to water vapor diffusion depends on the moisture content of the ambient air. The advantage of such vapor retarders is that they allow an accelerated drying of a structure if water has penetrated into the structure, because they are more open to diffusion at high moisture contents, and therefore it is possible for moisture to escape. When the moisture content of the air is low, for example in winter, if a water vapor diffusion current moves from the inner side toward the outer side, these vapor retarders have higher Sd values and inhibit the diffusion of water vapor.
A moisture-variable film with a resistance to water vapor diffusion which is moisture-dependent is described, for example, in WO 96/33321 A1. The Sd values of the known film vary from 2 m to 5 m at 30% to 50% relative humidity, up to <1 m at 60% to 80% relative humidity. The film described is designed for use in the central and northern European climate on the interior side.
In climates with warm winters and hot, humid summers, the diffusion current, however, is reversed. In this case, higher vapor pressures occur in the outside air than in the interior. This is particularly the case if the air indoors is conditioned. There is a risk of condensation forming in this case as well. For this reason, diffusion-inhibiting layers are installed on the outer surface of an insulated building structure in hot, humid climates. Climates that have both hot and humid summers and cold winters and, for example, are found at high altitudes in various tropical and subtropical countries, are particularly critical in this case. It is necessary to use combinations of protective layers customized to the local climate, such as vapor retarders with webs for roofs and/or facades.
If protective layers which are designed for use in climatic conditions in temperate climates are used in other climates, dew may form, and in the worst case the structure may fail. To prevent this, different protective layers must be used in practice on the outer side and inner side, and these must be customized to the climatic conditions. If the incorrect protective layers are used, or if no protective layers are used, this can contribute to a reduction in the useful life of the building, and to an increase in energy consumption. This is discussed below.
Hygrothermal simulations can be used to assess the moisture resistance of insulated building structures, and can be carried out, for example, using the WUFI® 5.2 method developed by the Fraunhofer Institute for Building Physics for calculating the transient heat and moisture transport in components. The WUFI® 5.2 program offers the possibility of, among other things, selecting and specifically determining different climates, material data, orientations of buildings and more.
A typical steep roof structure 1 is shown schematically in FIG. 1, and has the structure detailed below, beginning with the outer roof cladding:
Layer/Material(from outer side to inner side)Thickness [m]Roof tile (2)0.01Air layer (3)0.025Protective layer, outer side (4)0.001Glass wool layers (5a-c)0.140Protective layer, inner side (6)0.001Air layer (7)0.025Gypsum plasterboard (8)0.0125
FIG. 2 schematically shows the layer structure of the roof structure 1 described above. The following refers to FIG. 2.
Hygrothermal simulations were created using the WUFI® 5.2 Pro program for the steep roof structure 1, and the moisture resistance of the steep roof structure was evaluated. The complexity of the results attainable with this simulation program made it necessary to define specific evaluation criteria for the given application. As part of the invention, the moisture content of the thermal insulation adjacent to a non-absorbent boundary surface and/or protective layer, such as a vapor retarder or roof membrane, has been taken into account as a decisive factor. For this purpose, the glass wool insulation (glass wool layers 5a-5c) with a total insulation thickness of 140 mm was divided by calculation, such that very thin layers of 1 mm at the boundary surfaces with the vapor retarders 4, 6 were considered separately.
Starting from the premise that the Sd value of the protective layer 4 (outer side) is 0.10 m and the Sd value of the protective layer 6 (inner side) is 20 m, a moisture content of not more than 8 g/m2 at the inner glass wool layer 5c, and on the outer glass wool layer 5a a maximum moisture amount of 16 g/m2 was determined in the simulation calculations that were performed for the climate region “Holzkirchen/Germany” under constant, unfavorable conditions (orientation: north; pitch: 38°; outer roof surface; radiation absorption from red roof tile; inner thermal resistance: roof; initial conditions: 0.8% relative initial moisture, averaged over the component; during the period from 1 Aug. 2009 until 1 Aug. 2013; two hour calculation intervals (reduced if there are convergence problems). Practical knowledge is available for the DIN-standard-compliant construction of the pitched roof structure 1, which proves that no damage occurs with the above-mentioned amounts of moisture, and therefore support the assessment that these maximum moisture contents are harmless. If protective layers with these Sd value combinations, which are very well suited for the climatic conditions in the temperate climate, are nonetheless used in other climates, harmful condensation can occur, leading to, at worst, the failure of the structure. For example, proceeding from condensation simulations for the climate region “Miami/USA” (very hot and humid outdoors), for the same construction of the pitched roof structure 1, the result is a maximum amount of moisture on the inner glass wool layer 5c of 565 g/m2 and on the outer glass wool layer 5a a maximum amount of moisture of 11 g/m2, which according to DIN 4108 is considered harmful in terms of structural physics. However, if the outer protective layer 4 and the inner protective layer 6 are replaced by each other, the results for the climate region “Miami/USA” are harmless maximum moisture contents in the glass wool layers 5a, 5c, of 5 g/m2 on the inner side and 4 g/m2 on the outer side.
This fact has to-date been borne out in building practice by the need to use different vapor retarders customized to the conditions on the outer side and the inner side. If improperly designed and/or if no vapor retarders are used, this contributes to the fact that the useful life of the building will be reduced and more energy consumption is to be expected.
However, if moisture-variable vapor retarders in the previously considered steep roof structure 1 (FIG. 1) are used, the following moisture values in the boundary layers of the protective layers 4, 6 are found by hygrothermal simulations as described above:
Amount ofSd valueAmount ofwater glass[m]Sd value [m]water glasswool layerprotectiveprotectivewool layer 5c5aClimatelayer 6layer 4(inner side)(outer side)region(inner side)(outer side)in [g/m2]in [g/m2]HolzkirchenVariable0.1525Holzkirchen20  Variable820Holzkirchen0.1Variable2762MiamiVariable0.1157Miami20  Variable28823Miami0.1Variable45
The use of a protective layer 6 (inner side) with a variable Sd value, and a protective layer 4 (outer side) with an Sd value of 0.1 for the climate region “Holzkirchen/Germany” leads to slightly elevated but acceptable moisture contents in the outer glass wool layer 5a, which is adjacent to the outer protective layer 4, constructed as a weather protection web. The use of the same protective layer 4, 6 for the climate region “Miami/USA” results in increased but acceptable moisture contents on the inner side. In contrast, if a protective layer 6 (inner side) with an Sd value of 20 m, and a protective layer 4 (outer side) with a moisture-variable Sd value are used, for the climate region “Miami/USA” the result is not only a very high water content of the inner glass wool layer 5c, but also an increase in the total water content of the construction, which is highly dangerous. The same Sd value combination for climate region “Holzkirchen/Germany,” in contrast, results in harmless moisture contents. As such, it is possible, merely with a certain variation/combination of Sd values of materials adjacent to the thermal insulation, to achieve a structure with no damage potential. Conversely, an incorrect material selection and/or incorrect installation situation carries a high risk of damage.
To make matters worse, with increasing industrialization in tropical climates, air conditioners are used, which can exacerbate the problem of condensation. As a result, the amounts of water encountered sometimes are increased by more than double, which can lead to failure of the structure due to moisture accumulation. Accordingly, in the prior art, there is general agreement that different protective layers/materials must be used on the inner side and on the outer side as protection against the weather. No protective layer is known from the prior art which can be used in different climatic regions worldwide. Also, there is no combination known in the prior art of a moisture-variable vapor barrier inside, and a diffusion-open web for roofs and/or facades outside, which can be used worldwide and/or regardless of climate.